1. Field of the Invention
The present invention relates to a polishing pad for use in chemical mechanical polishing.
2. Description of the Related Art
Chemical mechanical polishing (CMP) is a procedure for planarizing the surface of a substrate with a polishing pad. CMP is generally applied in polishing lens, mirrors, substrates of liquid crystal displays, silicon wafers, and oxidation and/or metal layers on silicon wafers.
Taking silicon wafers as an example, ingots of monocrystalline silicon are sliced first. The wafers are usually lapped to make them flat for subsequently chemical etching. A polishing process is required after the etching process. During the polishing process, a polishing pad together with slurry reacts chemically with the silicon atoms on the surface of the wafer to make the reacted surface softer than the underlying silicon. Furthermore, the reacted surface is continually wiped away causing fresh silicon to be exposed to the slurry and the polishing pad.
A conventional polishing pad comprises a base material comprising fibers. A polishing layer comprising porous elastomer such as polyurethane is also provided on or in the base material. By using pressure sensitive adhesive (PSA), the conventional polishing pads are secured to a polishing platen or head of a polishing machine. The pressure sensitive adhesive comprises a carrier film comprising polyester, for example, and has adhesive with a low fluidity on an upper side and a lower side of the carrier film, such adhesive being known as dual-sided adhesive. The adhesive on the upper side of the carrier film is configured to couple the base material of the polishing pad, and that on the lower side of the carrier film is to couple the polishing platen or head of the polishing machine.
Because the base material of the polishing pad comprises fibers, the content of the base material is not distributed evenly. The variations in the thickness of the base material are easily observed. Besides, the surface of the base material is not flat and is usually rough and undulant. Such features make the base material difficult to attach tightly and completely to the adhesive on the upper surface of the carry film of the pressure sensitive adhesive. Bubbles and vacant space are easily observed in an interface between the base material and the pressure sensitive adhesive. As a result, the slurrycan easily permeate into the interface between the base material and the pressure sensitive adhesive via the bubbles and vacant space. Therefore, the life span of the polishing pad is shortened. Additionally, when the polishing pad is replaced, residues of the pressure sensitive adhesive are easily left behind on the polishing platen or head and the residues of the pressure sensitive adhesive need to be removed and the duration of the time necessary for replacing polishing pad is lengthened. The effect and efficiency of chemical mechanical polishing are both reduced thereby.